Primary cell



June 17, 1969 R. E. DUMAS ET AL PRIMARY CELL Filed May 5. 1966 he J/M/ RNEYS B J 05$ o T D T NMAO T EUHO WD W ama WLD O M RN AAO RHD United States Patent US. Cl. 136-100 3 Claims ABSTRACT OF THE DISCLOSURE An improved magnesium-manganese dioxide primary cell is provided by applying an ultra thin film on the order of 1000 angstroms in thickness of palm oil to the inner surface of a magnesium base alloy can or anode. The cell uses a 4 to 5 normal aqueous solution of magnesium perchlorate as the electrolyte.

This invention relates to primary cells, and more particularly to a primary cell including a magnesium base alloy as the anode, an aqueous solution of magnesium perchlorate as the electrolyte, and a cathode comprising manganese dioxide.

Such a primary cell is known in the art, as for example, as taught in U.S. Patent No. 2,993,946. The system is desirable in that cells with a magnesium base alloy as the anode yield considerable electrical energy per unit of cell volume and weight. This makes them valuable as a portable power supply in new and more sophisticated communication equipment that require more input power in smaller packages. A difficulty encountered with such primary cells, however, is their relatively large delayed action. The delayed action is defined as the time required for a cell to reach an equipment dictated useable voltage level when it passes from the open circuit or no load condition to closed circuit conditions.

The general object of this invention is to materially shorten the delayed action of the magnesium-manganese dioxide cell systems. A particular object of this invention is to provide a magnesium-manganese dioxide cell system characterized by a minimum delayed action, good storageability, operation over a wide temperature range, mechanical ruggedness, good voltage regulation, and low cost.

It has now been found that the aforementioned objects can be attained by using a 4 to 5 normal aqueous solution of magnesium perchlorate as the electrolyte in the magnesium-manganese dioxide cell system; and by applying a thin film of palm oil, lanolin, or other compounds containing fatty acids, or esters of fatty acids to the inner surface of the magnesium base alloy can or anode. Additionally, in fabricating the primary cell where the cell is consolidated in accordance with normal procedures, it has been found advantageous to store the cell for periods ranging from 4 to 20 hours in an atmosphere humidified to saturation over 5 normal magnesium perchlorate. The cell is then reconsolidated and then sealed in conventional manner.

The invention can best be illustrated by the following example and accompanying drawing wherein is shown an enlarged cross sectional view of a magnesium-manganese dioxide cell according to the invention.

EXAMPLE Referring to the drawing, a dry cell of conventional design may be prepared as follows: a metallic anode 11 is provided in the form of a can of a standard N size, or other standard size. The anode 11 has the approximate composition 96.75% magnesium, 2% aluminum, 1% zinc, 0.15% calcium, and 0.10% manganese. This alloy composition is sometimes designated AZ21A. An

anode coating solution of one part by weight of palm oil to 17 parts by weight of benzene is then applied to the inner surface of the anode 11 at a temperature of 110 F. for 30 seconds. The anode 11 is then drained and air dried. An ultra thin film 12 of the order of 1000 angstroms in thickness is thus deposited on the inner surface of anode 11. The anode 11 hearing the film 12 is then lined with a separator 13 comprising an absorbent kraft paper about 3.5 mils in thickness. Within the compartment, of which the separator 13 now forms the outer wall, is a cathode mixture 14 of materials comprising a cathode depolarizer, an ingredient for increasing the conductivity of the composition, an electrolyte, and a corrosion inhibitor. The separator 13 keeps the anode 11 and cathode 14 apart while providing therebetween a low resistance path to the fiow of ions during the electrochemical process.

The mixture 14 including the cathode material and electrolyte, and referred to as the cathode mix, is prepared of the following constituents in the proportions indicated:

Electrolyte Normal magnesium perchlorate 4.4 Grams per liter lithium chromate 0.20

Cathode material Percent Manganese dioxide 86.4 Carbon black 9.1 Barium chromate 3.5 Magnesium hydroxide 1.0

Approximately 3.2 grams of the cathode mix is formed as a cylindrical slug or bobbin and inserted in the coated and paper lined anode 13 to form the cathode with sufficient pressure to attain contact among the anode, separator, and cathode mix. At this point in the fabrication process, the unsealed cell is stored for periods ranging from 4 to 20 hours in an atmosphere humidified to saturation over 5 normal magnesium perchlorate. A carbon rod 15 is then inserted into the mix 14 with the application of pressure to provide electrical connection thereto. An insulating top washer 16 is mounted on the carbon rod 15 providing an air space 19 between the washer 16 and the cathode mix 14. A metal contact cap 18 of brass is placed on carbon rod 15. A molten sealant is then poured onto the top washer which on cooling forms a hard wax layer 17 which seals the cell against moisture loss. When the anode and cathode are connected through an external load of 10 ohms for 2 minutes, and then through open circuit for 28 minutes, the cell is found to deliver milliamperes per square inch of anode area.

Cells made according to the example also provide a battery that has at 70 F., 30 hours of service with a maximum delayed action of less than 0.5 seconds occurring at some time within the first 1O discharge cycles; at 10 F., the battery provides about 10 hours of service with a delay ranging from 1 to 5 seconds on the first discharge cycle. No delayed action is detected on subsequent discharges at 10 F. Prior magnesium-manganese dioxide cells show a delay time of about 30 seconds at 70 F.

It is believed that the discharge reaction of the cell of the example is controlled by the film formed on the magnesium base alloy anode. The modified fabrication technique in the foregoing example apparently allows the hydrogen gas generated during the protecting film form ing process to escape without significantly affecting the cell moisture content. The application of pressure to the cell following storage corrects the component interface disturbances, and removes pockets or voids created by the etfervescence of the hydrogen gas.

The foregoing description is to be considered merely as illustrative of the invention and not in limitation thereof.

What is claimed is:

1. A primary cell comprising a magnesium base alloy as the anode, a 4 to 5 normal aqueous solution of magnesium perchlorate as the electrolyte, and a cathode material comprising manganese dioxide, the inner surface of the anode having thereon a thin film coating of palm oil on the order of 1000 angstroms in thickness.

2. A primary cell according to claim 1 wherein the magnesium base alloy consists in parts by weight of 96.75 parts magnesium, 2.0 parts aluminum, 1 part zinc, 0.15 part calcium, and 0.10 part manganese.

3. A primary cell according to claim 1 wherein the cathode material consists in parts by weight of 86.4 parts manganese dioxide, 9.1 parts carbon black, 3.5 parts barium chromate, and 1.0 part magnesium hydroxide.

References Cited UNITED STATES PATENTS 10 WINSTON A. DOUGLAS, Primary Examiner.

R. T. ROSENBURG,

Assistant Examiner.

US. Cl. X.R. 

